Color television receiving stations with projection screen



G. VALENSI June 27, 1967 COLOR TELEVISION RECEIVING STATIONS WITHPROJECTION SCREEN Filed April 27. 1965 2 Sheets-Sheet 1 m Eu Q Q U m SmH E 8:11. M .I m: m

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650K625 VAL I KW 44M June 27, 1967 COLOR TELEVISION RECEIVING STATIONSWITH PROJECTION SCREEN Filed April 27, 1965 G. VALENSI 3,328,518

2- Sheets-Sheet 2 (mem QoflGS VALMSI United States Patent Ofi ice3,328,518 Patented June 27, 1967 2 Claims. cl. 178-54) ABSTRACT OF THEDISCLOSURE An electro-opt-ico-mechanical device for producing aprojected television picture, in saturated colors corresponding to thereceived hue signal, comprising a source of collimated rays of polarizedlight going through three modulators controlled respectively by theblue, green and red components of said hue signal; further, an analyzerand a focussing lens to produce a bright colored spot. A disc bearing acircular assembly of small lenses rotates at a stabilized speed betweensaid spot and the hole of a large con-cave mirror followed by a smallerconvex mirror. The motion of the upper small lens produces, betweenthese mirrors, one line of bright colored spots the enlarged image ofwhich is one line of said projected television picture.

The present invention concerns an improvement in or modification of thecolor television receiving station described in US. Patent No. 2,990,449and represented on Figure 1 attached to the specification of saidpatent; the principle of said receiving station is illustrated by theappended FIGURES 1 and la.

The following signals are extracted from the received video-signals: L,luminance signal, corresponding to the brightness; C, hue signal,characterizing the hue (or dominant radiation) of the color; S,stauration signal proportional to the degree of saturation of saidcolor; t field synchronizing signal; t line synchronizing signal. On theprojection screen EP are superimposed, on each other (like on theappended FIGURE 1), a detached black and white picture of the televisedscene produced by a projector P controlled by the luminance weightedsignal L=L/S, and a coarse picture of said scene, in saturated colors,produced by another projector PC controlled by the hue signal C. Thesetwo projectors are synchronized with the scanning of said scene bysignal t, and t The projector PC is schematically shown on the appendedFIGURE la; 2 is a powerful source of white light at thefocus ofcollimating lens P is a polarizer and A is an analyzer crossed with P; ff f, are interferential color filters passing respectively either lightof saturated blue color f or light of saturated green color f or lightof saturated red color f K K K are transparent crystals becomingbirefringent when a voltage: corresponding to the blue component C ofthe hue signal C is ap plied to K or corresponding to the greencomponent C of the hue signal C is applied to K or corresponding to thered component C,. of the hue signal C is applied to K,; the electrodesof these juxtaposed crystals are the (hatched) metallized parts of theirfaces, parallel to pclarizer P, as shown at the right of FIGURE 1a; thenonhatched circle corresponds to collimating lens producing the parallelrays of white light going through polarizer P, then, through thetransparent parts of K K K then, through analyzer A, followed by colorfilters, fl]! fv, f1"

I is a focussing lens, concentrating the blue, or green, or red light,at its focus on projection screen EP, after reflection upon one of themirrors of rotating drum M having, along its periphery, a plurality ofmirrors making different angles with the axis of electric motor M themotion of which is synchronized by the field synchronizing signals t sothat these mirrors move the colored spot produced at the focus of lens 1along the successive lines of one field of the coarse colored picture ofthe televised scene.

The electro-optico-mechanical device shown on FIG- URE la can enlightsufficiently only a projection screen EP of small dimensions, theenlightment (expressed in lux, or of a foot lambert) being given by theformula:

1 B.S. 6 N.D.

N being the number of distinct elements of the coarse picture of thetelevised scene, B being the luminance of the light source 2, FIGURE 1a,expressed in stilbs (candelas per square centimeter), S being thesurface of lens 1 expressed in square centimeters, D being the length ofthe light-path from lens 1 to mirror drum Mt and further to the screenEP, expressed in meters; the coefficient 1/ 6-=l/2 1/ 3 is due to thefact that polarizer P absorbs one-half of the luminous flux emergingfrom lens 1 and to the fact that only one of the three crystals K K Kmay be active for certain colors.

The object of the present invention is an improvedelectro-optico-mechanical device, affording the possibility of using amuch larger projection-screen, for example in a theater (or in'auniversity amphitheater), as shown on FIGURE 1, enlighted by a powerfulsource of light, the color of which is modulated by three transparentcrystals K K K becoming birefringent under control of applied voltagescorresponding to the components C C C, of the hue signal C. i

The invention will be described hereafter, with reference to theappended drawings, in which:

FIGURES l and 1(a) show a vertical section of a theater where the largeprojection screen EP is enlighted by projector Pbn producing a detailedblack-and-white picture, upon which projector PC superimposes a coarsepicture in saturated colors,

FIGURE 2 shows the optical part of projector PC,

FIGURE 3 illustrates the modulation of the color of the light insidesaid optical part of projector PC,

FIGURE 4 shows the electronic arrangement for stabilizing the speed ofrotation of the disc D of said optical part of projector PC, said discbeing associated with the rotating mirror drum TRM of FIGURE 1.

The optical part of projector PC, as represented on FIGURE 2, comprises:

(1) the discD made of magnetic material, having along one circle, asmany lenses as there are lines in one field of the television coarsepicture of the televised scene, and having, along its circumference, aplurality of teeth d, d; only one lens 1 which is at the top of disc Dwhen said disc rotates under the action of electric motor 'M,,, is shownon FIGURE 2 or FIGURE 4; these teeth a. induce, in a coil B, a sinewave(of frequency f when disc D rotates; an oscillator (0, FIGURE 4),synchronized by the received line synchronising signals t produces asinewave at the frequency f of the scanning lines in the acceptedtelevision standards; the frequency f always greater than f is comparedto frequency f in a differential electronic arrangement DE, which soproduces a stabilizing signal s feeding an electromagnet EF forproviding a more or less greater braking action on magnetic disc D,

(2) an optical arrangement made of a very large concave mirror (MS,FIGURE 2) having a central hole in front of which the circle of smalllenses of disc D moves, the upper lens I, producing, between said largeconcave mirror MS and the associated convex mirror ms, a line ofsuccessive colored images of the powerful white light corresponding toone line of one field of the coarse ricture (in saturated colors) of thetelevised scene,.the :olor being modulated by the crystals K K K inertedbetween crossed polarizer P and analyzer A (FIG- J'RE 2).

FIGURE 1 is a vertical section of a theater-building \B'CD', the publicseating on the floor CD, in front of he projection screen EP. Pbn is theprojector for the letailed black-and-white picture of the televisedscene, :ontrolled by the luminance weighted signal L'=L/S, [11dsynchronized by signals 1, and t coming from the disant televisiontransmitter. TR M is a large mirror drum, 'otating at a speed of turnsper second in the direction )f the arrow, under the action of anelectric motor M0 .uspended 0n the ceiling AB of the theater and syn-:hronized by synchronizing signals t TRM having five nirrors (in Europe)or 6 mirrors (in United States of America), because the televisionstandards specify '50 icture fields in Europe, and 60 picture fields inUnited States of America. The color-projector PC, the optical part ofwhich is shown on FIGURE 2, is located behind :he wall BD supporting theprojection screen EP, its arge concave spherical mirror MS emerging ontop of ;aid projection screen. The enlarged image of the small :oloredline, produced by lens 1 between the mirrors MS and ms, is reflectedupon one mirror of rotating drum lRM, and produces further, on screenEP, one line of )ne field of the coarse picture in saturated colors ofthe :elevised scene; the paths of light coming out of projector Pbn, orout of projector PC are represented by dotted lines on FIGURE 1 thecolored light produced by PC sweeps the projection screen EP when motorM0 rotates in the direction of the arrow; this colored light mixes withthe white light produced by projector Pbn upon screen EP, whereby thedesired degree of color saturation is always obtained for each point ofthe final image of the televised scene.

In the American television standards, there are per second 60 interlacedpicture fields having each lines; therefore disc D (FIGURES 2 and 4)should have 2.63 small lenses (such as 1 with a small opaque spacecorresponding to the time interval during two successive picture-fields,and disc D should make 60 turns per second. In the European televisionstandards, there are per second 50 interlaced picture-fieldshaving eachin coil B will be: 270 =16,200 seesubstantially greater than f thepicture-scanning-lines frequency f is 15,625 secin the Europeanstandards, and disc D should have 320 teeth d along its circumference,so thatthe frequency f of the wave induced in coil B will be 32050=16,000 SECI'I, substantially greater than f Now will be consideredthe electric modulation of the color of the light by means of crystals(K K K of FIGURE 2, and the enlightment of projection screen EP ofFIGURE 1 by the colored light projector PC. X is a powerful source ofWhite light (electric discharge between electrodes within pressurizedxenon) absorbing an electric power of 6500 watts, located at the firstfocus F of a cold-elliptic-mirror M and at the center of a sphericalmirror m, a very great part of the heat being radiated in the directionof arrow f, at left of M g. At the second focus F of elliptic mirror Mis produced a very small image X (of source X) having a brightness B of95,000 ,stilbs. (because mirror. m1 superimposes to the electricdischarge X its image, and produces so a very bright small spot). X isalso the focus of collimating lens l and F110 is an anticaloric glassplate, so that lens 1 receives very little heat. P is a polarizer and Ais an analyzer crossed with P, both being perpendicular to the beam ofparallel white-light-rays produced by Mirrors (at 45 degrees) split thisbeam of light-rays in three parts going respectively through the three"colored-light-modulators A K f for saturated blue, A K f, for saturatedgreen, M, K, for saturated red-4 f 7, being interferential color filterspassing respectively-only blue, or green, or red monochromaticradiations, and A A h being transparent plates (for example in mica)producing a retardation of one quarter of wavelength for blue light k orfor green light A or for red light 7\,. Other mirrors (at 45 degrees)reconstitute a beam of parallel rays of colored.

light, going through analyzer A and further concentrated, 'by focussinglens on a point X", where'is produced a very bright small image X" ofsource X, in front of the upper small lens l vof rotating disc D.

The motion of lens I, forms, at a given instant, a line of real imagesX," of X, which is one line of one field of the desired coarse pictureof the televised scene (in saturated colors, determined by thebirefraction of K or K.,., or K,, at this instant); this line of coloredluminous spots X is formed between the large concave spherical mirrorMS, of center C and focus F, and the small convex mirror ms, of centre Cand focus (,0. ms produces, between F and go, a line of virtual images Xof the spots X and MS produces a much larger line ofreal images X, onprojection screen EP, after reflection on mirror drum TRM (FIGURE 1).This line of real images Xfl' oflamp X constitutes one line of one fieldof the desired coarse According to the American television standardspictures of 525 lines, aspect ratio 4/3, as the chrominance spec- E luxtrum (in the received video-signal) is only about one fourth of theluminance spectrum, the total number N of elements of the coarse coloredpicture of the tele vised scene is:

'S is the surface of the circle having, for circumference,

the edge of the large concave mirror MS, expressed in squarecentimeters; if the radius of this circumference is 75 centimeters, S=1r(75) =l7,662 cm. The brightness B of lamp X (absorbing a power of 6500watts) is 95,000 stilbs (candelas per square centimeter) and B/6=15,833.In order that the enlightment produced by the coarse picture, insaturated colors, of the televised scene uponthe projection screen EPshould be lux (or 10 foot lamberts), the length D of the light-pathbetween mirror MS and screen EP on FIGURE 1, expressed in meters must bein accordance with the formula:

so that D: 11 meters of elements of the coarse colored picture of thetelevised With the same large concave mirror MS having a useful surfaceS=17,662 cmf and with the same lamp X having a brightness B =95,000stilbs (or 6X 15,833), in order to obtain an enlightment of 100 lux (orfoot-lam'berts) upon the projection screen (EP, FIGURE 1), the length ofthe light-path D between mirror MS and said screen EP, expressed inmeters, must be in accordance with the formula:

meters These values of D (11 or 9 meters) are compatible with therelative positions of mirror MS and projection screen EP in a theater,as shown on FIGURE 1.

The voltages C C,,, C (corresponding to the blue, green, red componentsof the hue signal C) are, in case of FIGURE 2, not applied directly tothe electrodes of crystals (K K K as on FIGURE la, but are put inopposition with an appropriate (direct-current or continuous) biasingvoltage, in order to obtain alternating modulating voltages (V V Vapplied respectively to said crystals; only the linear part of thesquare-sinecharacteristic of FIGURE 3 [giving the intensity I of thelight emerging from analyzer A (FIGURE 2) as a function of thealternating modulating voltage V, account being taken of the presence ofthe quarter-waveplate A or M, or h FIGURE 2] is utilized. On FIGURE 2, KK or K is, for example, a cylinder of single crystal of dihydrogenpotassium phosphate, the bases of which are perpendicular to the C axis,and are parallel to the faces of the corresponding quarter-waveplatesand also parallel to the crossed polarizer P and analyzer A, the neutrallines of said crystals, as well as the neutral lines of said quarterwaveplates, being at 45 degrees from the privileged direction ofpolarizer P; metallized conductive frames (in shape of a rectanglethrough which pass the rays of white light collimated by lens onFIGURE 1) constitute the electrodes of the crystals (K K,,, K,), towhich are applied the alternating modulating voltages (V V Vcorresponding to the components of hue signal C.

For a modulating voltage V=O, the corresponding point of thecharacteristic of FIGURE 3 is the middle M of the linear part; as thelight goes through the crystal arallely to the c axis, and as there isno applied modulating voltage, the crystal produces no retardation, andthe intensity I of the light emerging from analyzer A has its mean valuecorresponding to the retardation (one quarter of a wave length, M4)produced by the corresponding quarter-waveplate. For the modulatingvoltage V maximum of the absolute value of the negative part of themodulating voltage V, the corresponding point on the characteristic is Mthe crystal produces a retardation nearly equal to \/4), whereas thecorresponding quarter-waveplate produces a retardation equal to \/4);the resultant is zero, and as analyzer A is crossed with polarizer P, nolight practically emerges from analyzer A. For the modulating voltage V(maximum of the positive part of the modulating voltage V), the crystalproduces a retardation nearly equal to \/4), which is so added to theretardation (+)\/4) produced by the corresponding quarter-waveplate; theresultant is M2, and the light emerging from analyzer A (crossed withpolarizer P) has then its maximum intensity.

While the invention has been illustrated and described as hereabove, itis not intended to be limited to the details shown, since variousmodifications and structural changes may be made without departing inany way from the spirit of the present invention. Without furtheranalysis, the foregoing will so fully reveal the gist of the presentinvention that others can, by applying current knowledge, readily adaptit for various applications without omitting features that, from thestandpoint of prior art, fairly constitute essential characteristics ofthe generic or specific aspects of this invention, and, therefore, suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. Color television receiving station, on the large projection screen ofwhich are superimposed a black-andwhite detailed picture of thetelevised scene and a coarse picture of said scene with saturated colorsproduced by transparent members associated with color filters andbecoming birefringent under control of voltages corresponding to theprimary components of the received hue signal, in which the projector,producing said coarse picture in saturated colors, comprises incombination:

a very powerful source of white light located at one focus of a coldelliptic mirror,

a collirnating lens, the focus of which coincides with the other focusof said elliptic mirror,

a polarizer, located behind said collimating lens,

mirrors for separating the beam of parallel rays of white light emergingfrom said polarizer, into three parts going respectively through threecolored-lightmodulators, each comprising one of said transparent memberswith, on one side, an interferential color filter, passing only light ofsaturated (blue, or green, or red) color, and with, on the other side, acrystalline-plate producing a fixed retardation of a quarter of thewavelength of said light of saturated color,

other mirrors bringing close together the rays of colored lightsemerging from said modulators, for building a beam of parallel rays of alight having the color corresponding to the received hue signal, to theprimary components of which correspond the voltages a plied to saidtransparent members,

an analyzer crossed with said polarizer, and perpendicular to saidparallel rays of colored light, and followed by a focussing lens forproducing a small colored image of said source of white light,

an optical arrangement comprising a very large concave spherical mirrorwith a central hole and a smaller convex mirror in front of said hole,

a rotating disc made of a magnetic material, having a plurality of teetharound its circumference, and bearing a circular assembly of smalllenses, successively moving in front of said hole of said concavemirror, whereby the upper small lens, enlighted by said colored image ofsaid source of white light, produces between said concave and convexmirrors, a line of colored luminous s-pots corresponding to one line ofone field of said coarse picture of the televised scene,

a coil positioned in front of said teeth of said disc and in which isinduced a sine-wave of predetermined frequency when said disc rotates atits nominal speed,

a difierential electronic arrangement for stabilizing the speed ofrotation of said disc bearing said small lenses,

and a rotating mirror drum, fixed on the shaft of a motor controlled bythe received field synchronizing signals, and upon which is reflectedthe enlarged image of said line of colored luminous spots beforereaching said large projection screen.

2. Color television receiving station in accordance with claim 1, inwhich said differential electronic arrangement for stabilizing the speedof rotation of said disc bearing said small lenses and having said teetharound its circumference, comprises:

an electric motor for driving continuously said disc,

an oscillator controlled by the received line synchronizing signals, forgenerating a sine wave at the frequency f of said signals,

said coil, positioned in front of said teeth of said disc, and in whichis induced a sine-Wave at a frequency f slightly greater than andvarying more or less when said disc rotates at a speed greater orsmaller than its nominal speed,

a differential electronic arrangement, energized by said sine-waves offrequencies f and f respectively, for producing a correcting signal,

and an electromagnet, energized by said correcting signal, andpositioned in front of said disc of magnetic material, in order to act,more or less on said disc, as a magnetic brake, whereby the upper smalllens of said discmoves, in front of the central hole of said 7 largeconcave mirror, substantially along a rectilinear.

path and with a stabilized predetermined speed.

References Cited UNITED STATES PATENTS JOHN W. CALDWELL, Acting PrimaryExaminer.

J. A. OBRIEN, Assistant Examiner.

1. COLOR TELEVISION RECEIVING STATION, ON THE LARGE PROJECTION SCREEN OFWHICH ARE SUPERIMPOSED A BLACK-ANDWHITE DETAILED PICTURE OF THETELEVISED SCENE AND A COARSE PICTURE OF SAID SCENE WITH SATURATED COLORSPRODUCED BY TRANSPARENT MEMBERS ASSOCIATED WITH COLOR FILTERS ANDBECOMING BIREFRINGENT UNDER CONTROL OF VOLTAGES CORRESPONDING TO THEPRIMARY COMPONENTS OF THE RECEIVED HUE SIGNAL, IN WHICH THE PROJECTOR,PRODUCING SAID COARSE PICTURE IN SATURATED COLORS, COMPRISES INCOMBINATION: A VERY POWERFUL SOURCE OF WHITE LIGHT LOCATED AT ONE FOCUSOF A COLOR ELLIPTIC MIRROR, A COLLIMATING LENS, THE FOCUS OF WHICHCOINCIDES WITH THE OTHER FOCUS OF SAID ELLIPTIC MIRROR, A POLARIZER,LOCATED BEHIND SAID COLLIMATING LENS, MIRRORS FOR SEPARATING THE BEAM OFPARALLEL RAYS OF WHITE LIGHT EMERGING FROM SAID POLARIZER, INTO THREEPARTS GOING RESPECTIVELY THROUGH THREE COLORED-LIGHTMODULATORS, EACHCOMPRISING ONE OF SAID TRANSPARENT MEMBERS WITH, ON ONE SIDE, ANINTERFERENTIAL COLOR FILTER, PASSING ONLY LIGHT OF SATURATED (BLUE, ORGREEN, OR RED) COLOR, AND WITH, ON THE OTHER SIDE, A CRYSTALLINE-PLATEPRODUCING A FIXED RETARDATION OF A QUARTER OF THE WAVELENGTH OF SAIDLIGHT OF SATURATED COLOR, OTHER MIRRORS BRINGING CLOSE TOGETHER THE RAYSOF COLORED LIGHTS EMERGING FROM SAID MODULATORS, FOR BUILDING A BEAM OFPARALLEL RAYS OF A LIGHT HAVING THE COLOR CORRESPONDING TO THE RECEIVEDHUE SIGNAL, TO THE PRIMARY COMPONENTS OF WHICH CORRESPOND THE VOLTAGESAPPLIED TO SAID TRANSPARENT MEMBERS, AN ANALYZER CROSSED WITH SAIDPOLARIZER, AND PERPENDICULAR TO SAID PARALLEL RAYS OF COLORED LIGHT, ANDFOLLOWED BY A FOCUSSING LENS FOR PRODUCING A SMALL COLORED IMAGE OF SAIDSOURCE OF WHITE LIGHT, AN OPTICAL ARRANGEMENT COMPRISING A VERY LARGECONCAVE SPHERICAL MIRROR WITH A CENTRAL HOLE AND A SMALLER CONVEX MIRRORIN FRONT OF SAID HOLE, A ROTATING DISC MADE OF A MAGNETIC MATERIAL,HAVING A PLURALITY OF TEETH AROUND ITS CIRCUMFERENCE, AND BEARING ACIRCULAR ASSEMBLY OF SMALL LENSES, SUCCESSIVELY MOVING IN FRONT OF SAIDHOLE OF SAID CONCAVE MIRROR, WHEREBY THE UPPER SMALL LENS, ENLIGHTED BYSAID COLORED IMAGE OF SAID SOURCE OF WHITE LIGHT, PRODUCES BETWEEN SAIDCONCAVE AND CONVEX MIRRORS, A LINE OF COLORED LUMINOUS SPOTSCORRESPONDING TO ONE LINE OF ONE FIELD OF SAID COARSE PICTURE OF THETELEVISED SCENE, A COIL POSITIONED IN FRONT OF SAID TEETH OF SAID DISCAND IN WHICH IS INDUCED A SINE-WAVE OF PREDETERMINED FREQUENCY WHEN SAIDDISC ROTATES AT ITS NOMINAL SPEED, A DIFFERENTIAL ELECTRONIC ARRANGEMENTFOR STABILIZING THE SPEED OF ROTATION OF SAID DISC BEARING SAID SMALLLENSES, AND A ROTATING MIRROR DRUM, FIXED ON THE SHAFT OF A MOTORCONTROLLED BY THE RECEIVED FIELD SYNCHRONIZING SIGNALS, AND UPON WHICHIS REFLECTED THE ENLARGED IMAGE OF SAID LINE OF COLORED LUMINOUS SPOTSBEFORE REACHING SAID LARGE PROJECTION SCREEN.